Heretofore, an Al.sub.2 O.sub.3 -TiC-based material having superior wear resistance has generally been used as high-speed cutting ceramic tools. These tools, however, are not suitable for use in high-speed intermittent cutting such as milling, in which the tip is always subjected to thermal shock and mechanical shock, because of their insufficient thermal and mechanical shock resistances.
In recent years, Si.sub.3 N.sub.4 which is superior in toughness, mechanical strength and hardness and which has thermal shock resistance due to the fact that the thermal expansion coefficient thereof is as small as 3.5.times.10.sup.-6 /.degree.C., has received increasing attention as a ceramic material suitable for high-speed intermittent cutting. However, in commercially producing ceramic tools using Si.sub.3 N.sub.4, the following problems are encountered.
(1) Wear resistance is poor.
(2) Crater wear is large in the case of steel cutting.
(3) A hot press method is needed, since Si.sub.3 N.sub.4 is difficult to sinter, leading to undesirably high production costs.
Thus various investigations have been made to overcome the foregoing problems. Japanese Patent Application (OPI) No. 32377/81 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"), for example, discloses a cutting tool material comprising 5 to 40% by weight at least one member of TiC, TiN and TiCN, 10% by weight or less at least one member of AlN, oxides of rare earth elements, and six other materials (i.e., Al.sub.2 O.sub.3, MgO, SiO.sub.2, Fe, Co and Ni), the remainder being Si.sub.3 N.sub.4. Japanese Patent Application (OPI) No. 85481/80 discloses a throw-away tip comprising a sintered body mainly of Si.sub.3 N.sub.4 which is hot-pressed, and a coating layer of at least one of Al.sub.2 O.sub.3 and AlON provided on the surface of the sintered body. The former cutting tool, however, is not improved in wear resistance to the extent desired although the crater wear is reduced. In the latter cutting tool, the coating layer has an undesirable tendency to peel because of a large difference in the coefficients of thermal expansion between the Si.sub.3 N.sub.4 and the coating material. Moreover, both the former and latter ceramic tools require a hot press method for the production thereof, increasing their production costs. These materials, therefore, are of low practical value for use in the mass-production of cutting tools.